Field of the Invention
The present invention relates to a toner for developing electrostatically charged images in an image forming method, such as electrophotography or electrostatic printing, and a method for producing a toner.
Description of the Related Art
Recently, copiers and printers have been used in new market regions, and have been also used under different environments. Such circumstances require higher speed printing and high stability of images. For example, printers, which have been used mainly in offices traditionally, are used under severe environments at high temperature and high humidity. Printers using a high-speed one-component developing scheme have been receiving attention to satisfy requirements for a reduction in size, an increase in speed, and higher stabilization. The toner for the one-component developing scheme contacts a charging member less frequently compared to the toner for the two-component developing scheme using a carrier. Accordingly, a relatively large stress should be applied to the toner for the one-component developing scheme to be charged at a predetermined amount of charging. To satisfy these requirements, the durability of the toner and the stability of the charging performance irrespective of different environments should be enhanced not only under normal environments but also under environments at high temperature and high humidity.
Addition of a charge controlling agent to a toner has been traditionally examined to attain stabilization of charge, higher quality of images, and maintenance of image quality even after output of a large number of prints. Especially, toners containing a charge controlling resin are effective. For example, Japanese Patent Application Laid-Open No. 2012-256044 suggests a toner containing a charge controlling resin having a benzyloxysalicylic acid structure. Such a toner has high charging properties, and can suppress a reduction in fluidity even after storage under high temperature and high humidity, attaining stable charging performance. Japanese Patent Application Laid-Open No. 2011-137967 suggests a toner including a toner particle containing a resin capable of generating electricity, and resin particles adhering to the surface of the toner particle and being capable of dissipating charges. Such a toner keeps the charge density on the surface thereof appropriately low. This low charge density suppresses electrostatic aggregation of toner particles if an external additive is buried into toner particles after output of a large number of prints, barely causes deficits in images, and enhances durability under normal environments.
Unfortunately, this toner has insufficient stability of charging performance and durability under severe environments. Particularly, if the toner is used in printing at a higher process speed, the durability after output of a large number of prints is insufficient and stability of images is unsatisfactory under environments at high temperature and high humidity.